Research Papers

The Temperature-Dependent Viscoelastic Behavior of Dielectric Elastomers

[+] Author and Article Information
Jingkai Guo

Department of Mechanical Engineering,
The Johns Hopkins University,
Baltimore, MD 21218
e-mail: jguo19@jhu.edu

Rui Xiao

Department of Mechanical Engineering,
The Johns Hopkins University,
Baltimore, MD 21218
e-mail: rxiao4@jhu.edu

Harold S. Park

Department of Mechanical Engineering,
Boston University,
Boston, MA 02215
e-mail: parkhs@bu.edu

Thao D. Nguyen

Department of Mechanical Engineering,
The Johns Hopkins University,
Baltimore, MD 21218
e-mail: vicky.nguyen@jhu.edu

1Corresponding author.

Contributed by the Applied Mechanics Division of ASME for publication in the JOURNAL OF APPLIED MECHANICS. Manuscript received May 4, 2015; final manuscript received June 12, 2015; published online June 25, 2015. Editor: Yonggang Huang.

J. Appl. Mech 82(9), 091009 (Sep 01, 2015) (9 pages) Paper No: JAM-15-1218; doi: 10.1115/1.4030850 History: Received May 04, 2015; Revised June 12, 2015; Online June 25, 2015

In this paper, we investigated the temperature-dependent viscoelastic behavior of dielectric elastomers (DEs) and the effects of viscoelasticity on the electro-actuation behavior. We performed dynamic thermomechanical analysis to measure the master curve of the stress relaxation function and the temperature dependence of the relaxation time of VHB 4905, a commonly used DE. The master curve was applied to calculate the viscoelastic spectrum for a discrete multiprocess finite deformation viscoelastic model. In addition, we performed uniaxial creep and stress relaxation experiments and electrical actuation experiments under different prestretch conditions. The measured spectrum was applied to predict the experimental results. Generally, the model produced good quantitative agreement with both the viscoelastic and electro-actuation experiments, which shows the necessity of using a multiprocess relaxation model to accurately capture the viscoelastic response for VHB. However, the model underpredicted the electro-actuated creep strain for high voltages near the pull-in instability. We attributed the discrepancies to the complex boundary conditions that were not taken into account in the simulation. We also investigated the failure of VHB membrane caused by viscoelastic creep when prestretched and subjected to constant voltage loading. The experimental time to failure for the specimens decreased exponentially with voltage, which agreed well with the predictions of the model.

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Fig. 1

Images taken from actuation experiments: (a) and (b) equibiaxial prestretch, before and after actuation, and (c) and (d) uniaxial prestretch, before and after actuation

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Fig. 2

Model of electromechanical couple of DE membrane

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Fig. 3

Standard rheological model

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Fig. 4

Relaxation modulus as a function of time: (a) measured for different temperature and (b) shifted to a reference temperature of 20 °C to form a master curve

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Fig. 5

Shift factor as a function of temperature

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Fig. 6

(a) Distribution of discrete viscoelastic spectrum (τk,μkneq). (b) Comparison between master curves from experiments and the discrete model.

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Fig. 7

(a) Relaxation of the uniaxial tension engineering stress response and (b) uniaxial tension creep stretch response, comparing experiments and model prediction

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Fig. 8

Normalized stress as a function of stretch from uniaxial tension with different stretch rates, comparing experiments and model prediction

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Fig. 9

Relative stretch as a function of time (λ1pre=λ2pre=1.9), comparing results from experiments and simulation

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Fig. 10

Distribution of discrete spectra for cases 1–5

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Fig. 11

Voltage actuated creep simulation for cases 1–5 at 20 °C

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Fig. 12

Voltage actuated creep simulation for cases 1–5 at 60 °C

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Fig. 13

(a) Relative stretch from constant voltage actuation as a function of time, λpre = 1.7, V = 3.8, 4.0, 4.2, 4.4 kV, (b) relative stretch from constant voltage actuation as a function of time, λpre = 1.9, V = 3.6, 3.8, 4.0 kV, and (c) time to failure as a function of voltage




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